How to Improve OE Sub Bass Quality and Eliminate Vibrations

Kiwi Greg

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I painted the steel black behind the ports & mesh with some black CRC Zinc It

Handy stuff that was a perfect match for the Mags on my GT86 that I constantly kerbed :)
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I painted the steel black behind the ports & mesh with some black CRC Zinc It
Yeah, I thought about using matte black tape (that stuff that is like a blackboard) to cover the exposed steel, but I gave up after I realised the speaker material was off-white... May change my mind in the future.
 
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tadda

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Thanks for the correction. In my defense, it was very late when I made the drawings ... lol

@tadda here you go

Screen Shot 2020-05-09 at 11.18.47 PM.png
Thanks!

I updated my original post with corrected drawing...
 
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tadda

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Here are other options I also considered (replacing the 2" ports) which would secure to the narrow rear panel....

2" square grill cover

exhaust port cover.jpg


2" round grill cover

speaker grill cover.jpg
As I mentioned earlier there is also another alternative to adding a port and that would be to simply cover the rear cover panel 2" exhaust holes with a grill cover as shown above...This will also eliminate the need to cover the 3 elongated exhaust posts with mesh covering...

Those that already have installed the 2" ports can always replace them with a grill cover...
 
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tadda

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Some additional improvement tips (update added to original post):

For those that have completed this project, which involved lining the walls of the speaker enclosures, placing foam insulation between enclosure and narrow rear panel, and adding exhaust ports, I've also identified that there is one final area that needs to be addressed....

I discovered this after implementing all these other improvements, thus allowing me to significantly increase volume along with raising bass EQ settings...What I found was that there was some exhaust port energy escaping from under the long narrow rear panel (which as I show in a few pics below) causing the rear floor panel cover to vibrate...Keep in mind that this is yet another design problem which causes the floor panel cover to vibrate where in-turn this vibrational energy is transferred to the cargo areas' side and back panels causing them to vibrate as well...

The solution here was to apply some adhesive back foam to the areas show below which eliminated any energy transfer under the rear floor panel cover...

Shown below, I first applied 1.5"d x 4" L x 0.25" h adhesive backed foam strips above and below both exhaust ports
to isolate them further from the top cover and floor....

subwoofer 7b ported rear panel insulation strip.jpg


Next, the image below shows where some exhaust energy from the 3 elongated ports was also being released under the large rear floor panel cover causing it to vibrate greatly...With the floor panel removed simply place your hand under the narrow panel and you'll see / feel the exposed gap ...

subwoofer 2a narrow rear panel exhaust port leak.jpg


Below shows locations where 2 adhesive back foam strips were applied to underside of exposed narrow rear panel ...The left adhesive backed foam strip was 1.5"D x 11" L x 0.25" H and the right foam strip is 1.5"D x 6" L x 0.25" H...This essentially sealed off the gap where the exhaust energy was also being channeled...
subwoofer 2a narrow rear panel foam strips.jpg


As a result the large rear floor panel cover vibration has pretty much been eliminated and side and rear trunk panels no longer vibrate during low bass / high volume music passages....

As far as materials, I used Noico RED 315 mil Sound Insulation , which I already had available for beginning my next project of eliminating front door speaker vibrations ....
 
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tadda

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And finally, after all the improvements made, which are outlined in this thread, here are my latest settings below...I can now increase volume to 2/3 of max and significantly raise low bass EQ settings without experiencing any low bass distortions or vibrational noise...Bass is deeper, clearer, and punchier, with far less distortion...The Harmon Kardon Subs are actually very good speakers and I currently have no desire to replace them anytime soon...

Here are my current audio settings:
  • ASD / Active Sound Design (off - using Bimmercode)
  • Surround (off)
  • Speed Volume (+4)
  • Balance: (0)
  • Fade: (front +2)
  • Broad Bass (+4)
  • Broad Treble (-1)
  • Equalizer (shown below)
This are my latest EQ settings (below) after improvements made to current OE Subwoofer system...

View attachment 26054

And a big thanks to: @JasonO @30MilesOffshore @Kiwi Greg @stacyoz @Reppunkamui @2k20HTownMKV for your contributions! :thumbsup:
 

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That's good to hear! Thanks for the update. I finally pulled the trigger and ordered some low pass filters today. Will post up my findings once I get them installed. Thanks again!
 

Kiwi Greg

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And finally, after all the improvements made, which are outlined in this thread, here are my latest settings below...I can now increase volume to 2/3 of max and significantly raise low bass EQ settings without experiencing any low bass distortions or vibrational noise...Bass is deeper, clearer, and punchier, with far less distortion...The Harmon Kardon Subs are actually very good speakers and I currently have no desire to replace them anytime soon...

Here are my current audio settings:
  • ASD / Active Sound Design (off - using Bimmercode)
  • Surround (off)
  • Speed Volume (+4)
  • Balance: (0)
  • Fade: (front +2)
  • Broad Bass (+4)
  • Broad Treble (-1)
  • Equalizer (shown below)
This are my latest EQ settings (below) after improvements made to current OE Subwoofer system...

View attachment 26054

And a big thanks to: @JasonO @30MilesOffshore @Kiwi Greg @stacyoz @Reppunkamui @2k20HTownMKV for your contributions! :thumbsup:
Thanks Heaps for putting all the info up tadda :thumbsup:

I have ordered the tape you referenced in your previous post, I guess I might get it in 6-8 weeks, we shall see..

I figured it would be best to get the right stuff for that job
 
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tadda

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Thanks Heaps for putting all the info up tadda :thumbsup:

I have ordered the tape you referenced in your previous post, I guess I might get it in 6-8 weeks, we shall see..

I figured it would be best to get the right stuff for that job
The strips are actually cut from 15.7" x 9.8" adhesive backed foam pads used to surpress vibrations and noise....I intend to use the remaining pads to insulate the front doors which will be my next project....
 

Kiwi Greg

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The strips are actually cut from 15.7" x 9.8" adhesive backed foam pads used to suppress vibrations and noise....I intend to use the remaining pads to insulate the front doors which will be my next project....
Sorry yes that is what I meant & figured you had some other tricks up your sleeve so grabbed a box of it thanks :thumbsup:
 

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And finally, after all the improvements made, which are outlined in this thread, here are my latest settings below...I can now increase volume to 2/3 of max and significantly raise low bass EQ settings without experiencing any low bass distortions or vibrational noise...Bass is deeper, clearer, and punchier, with far less distortion...The Harmon Kardon Subs are actually very good speakers and I currently have no desire to replace them anytime soon...

Here are my current audio settings:
  • ASD / Active Sound Design (off - using Bimmercode)
  • Surround (off)
  • Speed Volume (+4)
  • Balance: (0)
  • Fade: (front +2)
  • Broad Bass (+4)
  • Broad Treble (-1)
  • Equalizer (shown below)
This are my latest EQ settings (below) after improvements made to current OE Subwoofer system...

View attachment 26054

And a big thanks to: @JasonO @30MilesOffshore @Kiwi Greg @stacyoz @Reppunkamui @2k20HTownMKV for your contributions! :thumbsup:
Looks good man! Iā€™m seriously curious as to how your system is handling what you listen to as it isnā€™t friendly to poor subwoofer performance.

Let me know how the Noico red works out. Iā€™m installing CLD and thinsulate, but donā€™t want to put thinsulate in my outer door skins as while it is somewhat hydrophobic, it is highly porous. Iā€™m going to squeeze some in the inner skin and interior panel, but I donā€™t think Iā€™ll get the best coverage while keeping full thickness. If it works, I may install a layer in the outer skin over the CLD I added.
 
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tadda

tadda

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Looks good man! Iā€™m seriously curious as to how your system is handling what you listen to as it isnā€™t friendly to poor subwoofer performance.

Let me know how the Noico red works out. Iā€™m installing CLD and thinsulate, but donā€™t want to put thinsulate in my outer door skins as while it is somewhat hydrophobic, it is highly porous. Iā€™m going to squeeze some in the inner skin and interior panel, but I donā€™t think Iā€™ll get the best coverage while keeping full thickness. If it works, I may install a layer in the outer skin over the CLD I added.
My musical tastes are very broad from rock, pop, EDM, alternative, classic, jazz etc.....that said, the Techno and EDM tracks really tests the subs limits and is what I enjoy listening to the most....

This latest album (below) I've been using to setup and test the sound system and particularly the subwoofers has allowed me to isolate all the vibrations, distortions, and rattles....I spent nearly 2 hrs in my Supra yesterday enjoying the entire album at 2/3 max volume and it sounded amazing...And damn the bass is tight and deep now....

Ethereal Techno #008 - favorite tracks are 1,3,5,6,9,19,20

As I've mentioned a few times already, to my surprise and delight the HK Subs are actually very good once you remove all the other physical design warts in the system! Lining the sub enclosure walls with speaker wadding and adding the exhaust port made a huge difference in overall sound quality...The rattles and vibrations also contributed quite a bit to poor sound quality which are gone now...

Next up are the doors and yes I'll definitely keep you posted and please do the same....
 
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JasonO

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My musical tastes are very broad from rock, pop, EDM, alternative, classic, jazz etc.....that said, the Techno and EDM tracks really tests the subs limits and is what I listening to the most....

This latest album (below) I've been using to setup and test the sound system and particularly the subwoofers has allowed me to isolate all the vibrations, distortions, and rattles....I spent nearly 2 hrs in my Supra yesterday enjoying this album at 2/3 max volume and it sounded amazing...

Ethereal Techno #008

As I've mentioned a few times already, to my surprise and delight the HK Subs are actually very good once you remove all the other physical design warts in the system! Lining the sub enclosure walls with speaker wadding and adding the exhaust port made a huge difference in overall sound quality...

Next up are the doors and yes I'll definitely keep you posted and please do the same....
If you are doing the doors, Iā€™d grab a few feet of decent CLD as the inner skin could use some help. I plan to have thinsulate and CLD in the doors and everything behind the seats within reason. If Iā€™m not happy, I will have enough to do the roof in both and CLD on the floor. For obvious reasons Iā€™m not doing them this round.

Know that you will need to pull a lot harder than you think compared to the rest of the clips to free up the clip by the door lock pin up top. Saving it for last has worked for me, but the amount of force required was unnerving the first time I did. The rest of the gotchas are covered vaguely enough in the Bavsound video.

Currently the state of my Supra:
6BC1F5F5-F17F-483A-820A-2D131D6F9A39.jpeg
2015F2B2-BA44-420B-99C4-A7DEB2D39987.jpeg
0EB8D60A-B984-484E-A39E-0A802D38A53F.jpeg
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